1. Field of the Invention
The present invention relates to a polymer electrolyte membrane, a membrane electrode assembly, and a fuel cell.
2. Description of the Related Art
Japanese Patent No. 3,921,997 discloses a polymer electrolyte membrane having a micro-phase separation structure formed of a block copolymer. The polymer electrolyte membrane includes an ion conductive domain including an ion conductive block and a non-ion conductive domain including a non-ion conductive block.
When a polymer membrane of this type includes ion conductive domains with a network micro-phase separation structure, the ion conductive domains have high continuity and have high ion conductivity.
However, there has been a problem that in order to maintain high continuity, a network micro-phase separation structure generally needs to be constituted by a block copolymer including an ion conductive block at a high volume fraction, which makes the strength of the polymer electrolyte membrane insufficient.
In order to allow the polymer electrolyte membrane to have a higher strength, when the volume fraction of a non-ion conductive block in the block copolymer is increased, the micro-phase separation structure does not form a network, so that the ion conductivity is reduced.